The maintenance of the thickness of ice is an important consideration in the management of commercial skating rinks. For indoor skating facilities, the ice is maintained preferably at a targeted thickness of approximately 25- to 40-mm (1.0- to 1.5-in.) and a temperature of −7 to −4° C. (20 to 24° F.). An ice sheet with a thickness that is substantially below this target range is at risk to break apart, with the possible consequence of injuring participants or postponing, delaying or canceling an event. The importance of maintaining ice at an appropriate thickness has led the National Hockey League (NHL), for example, to require NHL rink managers to report the ice thickness before and after each game. Recently, the National Collegiate Athletic Association (NCAA) has mandated that a survey of the ice thickness of the ice sheet at tournament venues be measured before each tournament game.
As the thickness increases substantially above the targeted thickness, the surface temperature of the ice may become undesirably high due to the conductive temperature gradient through the ice thickness. The skating surface may thereby become unduly soft and adversely affect the performance of participant skaters. The temperature of an overly thick ice sheet may be brought into the preferred temperature range by further sub-cooling the ice sheet, but this requires additional expenditure in refrigeration costs.
Ice thickness is also a factor in the management of outdoor rinks. Safety remains a factor in the maintenance of passively cooled rinks. Furthermore, refrigeration cooled outdoor rinks are becoming more common, and are subject to the same safety and energy consumption metrics as with indoor rinks.
An accepted practice for the measurement of ice thickness at commercial or municipal skating facilities is to drill a hole through the ice until the bit contacts the substrate below, temporarily mark the bit flush with the upper surface of the ice sheet, remove the bit, measure the distance between the tip of the bit and the temporary mark with a ruler or tape measure, and record the result on a sheet of paper. The procedure is repeated at several points on the ice sheet. The procedure is time consuming and labor intensive, and prone to the errors from a variety of sources including drilling the hole too deep (inadvertent penetration of the substrate) or not deep enough (sensing compacted ice rather than concrete), erroneously marking the drill bit, misreading of the tape or ruler, and the erroneous recording of the thickness measurement. Furthermore, in some instances the hole may cause local stress gradients that may cause the ice surface to pock under the rigors of use, thereby causing a hazard.
Moreover, the marked drill bit technique is not readily applicable to all ice facilities. Rink floors are typically configured in one of three ways. A first configuration is to imbed refrigeration piping in a concrete slab, thus enabling the venue to be utilized for purposes other than skating by merely melting the ice and draining off the water residual. A second configuration, appropriate for dedicated ice rinks, is to imbed refrigeration piping in a sand or granular substrate. A third configuration involves laying the refrigeration piping exposed on a substrate (concrete, granular, earthen or otherwise) and flooding the floor for direct contact between the ice and the refrigeration piping. An example is the so-called “mat system,” wherein long, narrow banks of refrigeration piping (e.g. 1-m wide by 15-m long) are laid out side by side and hooked to a common refrigeration supply header. This type of configuration finds utility for seasonal venues, where the rink is dismantled at the end of a season.
The marked drill bit technique is generally or variably applicable only to the first configuration. For the second configuration, the operator cannot reliably detect when the ice sheet has been penetrated. For the third configuration, even where a floor of sufficient hardness is implemented, there is a danger of damaging the refrigeration piping. As a workaround, operators of sand bottom facilities may install metal plates or concrete blocks at select locations on the substrate for the purpose of receiving the tip of the drill bit during in a measurement check. Operators of surface installed refrigeration may carefully select and mark locations where the piping will not be damaged. However, subsequent measurements are limited, and inspection of thickness in areas away from the pre-selected locations cannot be performed.
The implementation of acoustical devices in the measurement of ice thickness is known. Hereinafter, “acoustic” or “acoustical” refers generally to the acoustic spectrum, including infrasound, audible sound and ultrasound. See Ingard, “Fundamentals of Waves and Oscillations,” p. 298 (1988: Cambridge University Press). A body of literature exists, for example, disclosing devices and techniques for the detection of ice build up on vehicles or vehicle components such as aircraft members. U.S. Pat. No. 4,628,736 to Kirby et al. describes an apparatus and method wherein the reflection of transmitted acoustic waves through a thickness of ice on a vehicle member is transmitted from the vehicle member through the ice to the ice/air interface, where a portion of the acoustic signal is reflected back to the vehicle member for detection by a receiver. U.S. Pat. No. 5,095,754 to Hsu, et al. further discloses an improvement to this technique that enables the discernment of water at the air interface. U.S. Pat. No. 5,507,183 to Laure et al. compares an “uncontaminated” reflected signal through a vehicle member to a delayed “contaminated” signal reflected off the ice/air interface in making the thickness determination. U.S. Patent Application Publication No. 2003/0169186 to Vopat measures the composite thickness (ice and aircraft member) and discloses a method for subtracting the aircraft member thickness from the composite thickness to arrive at the ice thickness. What is common to the disclosures above is that the transmitting and receiving devices are imbedded in a dedicated application, and the thickness of the ice is determined from the bottom up, thereby relying on the ice/air or water/air interface to deliver a detectable reflected signal.
U.S. Pat. No. 5,557,047 to Koide discloses a thickness measuring device wherein a transmitter and a receiver are situated on one face of a medium and a reflector is situated on the opposing face of the medium. Kiode's measurement technique involves the measurement multiple reflections back and forth through the medium resulting from a single pulsed input, and is not well suited for configurations where the reflector highly attenuates the signal (e.g. a sand or granular substrates, or certain concrete or asphalt substrates).
Products exist on the market that provide an ultrasonic thickness measurement in a portable package. An example is the POCKETMIKE general purpose thickness gauge marketed by GE Inspection Technologies. Such devices are compact, portable and generally applicable to the thickness measurement of an ice medium. However, such devices suffer from a number of drawbacks. For example, a characteristic of available devices is that their response slows down as the unit becomes cooler. It has been observed that available devices eventually become temporarily inoperable as the unit cools under repeated contact with the ice. An operator must then wait for the unit to warm up again before resuming a series of readings. Available portable ultrasonic devices also lack means for locally and automatically logging a series of recorded measurements, thereby requiring an operator to scribe the readings. Existing units also are not configured for ease of operation when applied to the measurement of ice sheet thickness. The operator must bend over or kneel to operate the controls of the unit and to view the readout.
Given the importance of timely and accurate ice thickness associated with present ice thickness measurement techniques, a portable, non-destructive thickness measuring device configured for the rapid measurement and automatic recording of ice thickness would be welcome.